1. Field of the Invention
The present invention relates to an inverter device having an inverter function for converting DC to AC or a current type inverter device having a chopper function for controlling DC power and an inverter function for converting DC to AC. More particularly, it relates to an economical inverter device wherein economical thyristors are used instead of expensive transistors and a transistor is used for extinction of the thyristors.
2. Description of the Prior Arts
FIG. 1 shows the conventional inverter device wherein the reference (1) designates a DC power source; (2U+), (2V+), (2W+), (2U-), (2V-), (2W-) designate transistors; (3U+), (3V+), (3W+), (3U-), (3V-), (3W-) designate diodes. The pairs of the transistor (2U+) and the diode (3U+); transistor (2V+) and the diode (3V+); the transistor (2W+) and the diode (3W+); the transistor (2U-) and the diode (3U-); the transistor (2V-) and the diode (3V-); and the transistor (2W-) and the diode (3W-) are respectively connected in reverse parallel with each other. The pairs of the transistors (2U+), (2U-); the transistors (2V+), (2V-); and the transistors (2W+), (2W-) are respectively connected in series. Moreover, the collectors of the transistors (2U+), (2V+), (2W+) are connected to the positive side of the DC power source (1) and the emitters of the transistors (2U-), (2V-), (2W-) are connected to the negative side of the DC power source (1).
The reference (4) designates a load and three terminals (U), (V), (W) are respectively connected to the joint between the transistors (2U+), (2U-); the joint between the transistors (2V+), (2V-); and the joint between the transistors (2W+), (2W-). The bases of the transistors (2U+), (2V+), (2W+), (2U-), (2V-), (2W-) are connected to a base control device (5). The transistors are turned on by the base control device (5) for the periods shown in FIG. 2 wherein each shift of 120.degree. is given between the transistors (2U+), (2V+), (2W+) and each shift of 180.degree. is given between the transistors (2U+), (2U-) between the transistors (2V+), (2V-) and between the transistors (2W+), (2W-) to turn on these transistors by the base signals.
When the base signals are respectively inputted to the bases of the transistors in the conventional inverter device, the voltages shown in FIG. 3 are formed between the terminal (U), (V), (W) of the load (4). When the voltage of the DC power source (1) is given as Ed, the voltage "Ed" is applied between the terminals (U)-(V) and the voltage "-Ed" is applied between the terminals (V)-(W); and the voltage "Zero" is applied between the terminals (W)-(U) in the period (I) of FIG. 2 which corresponds to the period (I) of FIG. 3, since the transistors (2U+), (2W+), (2V-) are respectively in ON state.
The voltage "Ed" is applied between the terminals (U)-(V) and the voltage "Zero" is applied between the terminals (V)-(W); and the voltage "-Ed" is applied between the terminals (W)-(U) in the period (II) of FIG. 2 which corresponds to the period (II) of FIG. 3 since the transistors (2U+), (2V-), (2W-) are respectively in ON state. Thus, AC power source is fed from the DC power source (1) to the load (4).
Each of the diodes (3U+), (3V+), (3W+), (3U-), (3V-), (3W-) is used for passing the current passed by each of the transistors (2U+), (2V+), (2W+), (2U-), (2V-), (2W-) when each of these transistors is in OFF state. For example, when the transistor (2U+) is turned off, the current is passed by the diode (3U-). When the diode (3U-) is turned on, the potential of the terminal (U) of the load is the same with the potential in ON state of the transistor (2U-). Accordingly, the voltage waveform of FIG. 3 is not changed.
FIG. 4 shows the conventional current type inverter device wherein the reference (11) designates a DC power source; (12) designates a chopper connected to the DC power source (11); (13+), (13-) designate DC reactors connected to the chopper (12); (14) designates an inverter connected to the DC reactors (13+), (13-) and the DC power source (11); (15) designates a load connected to the inverter (14). The chopper (12) is formed with transistors (101) (102) for chopper function and diodes (103), (104). The inverter (14) is formed with transistors (105) to (110) and diodes (111) to (116). The reference (16) designates a control device for controlling bases of the transistors (101), (102), (105) to (110).
The operation of the current type inverter device will be illustrated.
The chopper (12) is to control DC power fed from the DC power source (11) through the DC reactors (13+), (13-) to the inverter (14). When ON signal is input from the control device (16) to the bases of the transistors (101), (102), the power is fed from the DC power source (11) through the transistors (101), (102) to the inverter (14). When OFF signal is input from the control device (16) to the bases of the transistors (101), (102), the transistors are tuned off to feed-back the power from the inverter (14) through the diodes (103), (104) to the DC power source (11). Thus, the chopper (12) controls the power fed from the DC power source (11) to the inverter (14) by controlling ON and OFF of the transistors (101), (102). The reactors (13+), (13-) operate to smoothen the feeding of the power.
The DC power fed from the chopper (12) through the DC reactor (13+), (13-) is converted by the inverter (14) into AC power to feed it to the load (15). The ON-OFF signal shown in FIG. 5 is input from the control device (16) to the bases of the transistors (105) to (110). In the mode (I) wherein the ON signal inputs the bases of the transistors (105), (110) and the OFF signal inputs the bases of the other transistors (101), (107), (108), (109), the DC power is fed through the DC resistor (13+), the transistor (105), the load (15), the transistor (110) and the DC reactor (13-). When it is changed from the mode (I) to the mode (II), the base signal of the transistor (105) is switched from ON signal to OFF signal and the base signal of the transistor (107) is switched from OFF signal to ON signal. In this condition, when a reactor component is included in the load (15), the current passing through the transistor (105) is passed from the negative side of the DC power source (11) through the diode (112), and the current is gradually reduced, whereas the current passing from the DC reactor (13+) through the transistor (107) to the load (15) is gradually increased. The current passing to the DC reactor (13+) can be maintained substantially constant. When the current passing from the transistor (107) to the load (15) is less than the current of the DC reactor (13+), the current is passed through the DC reactor (13+), the transistor (107), the diode (113) and the transistor (101) or through the DC reactor (13+), the transistor (107), the diode (113), the DC power source (11) and the diode (103) depending upon the condition of the chopper (12). The current passing through the transistor (110) is not changed. When the current passing through the diode (103) is zero and the current passing through the transistor (107) is the same with the current passing through the DC reactor (13+), the current is passed through the DC reactor (13+), the transistor (107), the load (15), the transistor (110) and the DC reactor (13-).
Thus, the transistors (105) to (110) and the diodes (111) to (116) in the inverter (14) are sequentially and repeatedly turned on and off to feed AC power to the load (15).
In the conventional inverter device or the conventional current type inverter device, many transistors are used as switching elements. The transistors are remarkably expensive in comparision with thyristors (SCR) used as switching element (the same current capacity).
However, the thyristors are not in OFF state even though the current to the gate is stopped, and accordingly the normal operation can not be expected only by replacing the transistors with thyristors and it is necessary to connect a complicated and expensive commutation circuit when the thyristors are used instead of the transistors.